The proposed series of experiments is designed to describe some of the factors and mechanisms associated with the formation of axonal sprouts in developing or regenerating neurons. In an attempt to determine the importance of axonal damage on collateral fiber sprouting, lesions are being made of the dorsal adrenergic bundle, and sprouting of the collateral fiber branch of the locus coeruleus to the cerebellum is being studied. In another study locus coeruleus nuclei are being transplanted to assorted brain sites in order to characterize some of the factors that may be associated with growth of axonal fibers. Other studies on mutant mice lacking Purkinje cells in the cerebellum may lead to a better understanding of the interaction between target cells and growing fibers. It is expected that the above studies will lead to a better understanding of the factors and processes associated with neuronal regeneration.